1. Field of the Invention
The present invention relates to an electronic display, and more particularly to a capacitive coupled non-volatile electronic display for field controllable light transmissible material such as liquid crystal.
2. Description of the Related Art
With great advance in the fabricating techniques of optoelectronics and semiconductor devices, flat panel displays (FPDs) have been substantially developed. Among the FPDs, a liquid crystal display (LCD) has become the mainstream display product due to space utilization efficiency and low power consumption. The LCD includes an LCD panel and a backlight module in most cases. Since the LCD panel cannot emit light, the backlight module disposed underneath the LCD panel is required to function as a planar light source.
Please refer to FIG. 1A, which is a schematic diagram of a conventional thin film transistor (TFT) LCD device. The LCD device includes an LCD panel 100a, a gate driving circuit (scan driving circuit) 40a for driving the word line WL, a source driving circuit (data driving circuit) 42a for driving the bit line BL. The LCD panel 100a includes two substrates (not shown) and liquid crystal molecules filled between these two substrates. With reference to FIG. 1A, one substrate (such as a lower substrate) is disposed with a plurality of word lines WL, a plurality of bit lines BL perpendicular to the word lines WL, and a plurality of thin film transistors (TFTs) 20a. Each of the TFTs 20a has a gate electrically connected to the corresponding word line WL, a source electrically connected to the corresponding bit line BL and a drain electrically connected to the corresponding liquid crystal cell 10a. The other substrate (such as an upper substrate) is disposed with a common electrode for providing a common voltage or connected to ground. By supplying scan control signals through the word lines WL and data signals through the bit lines BL, the TFTs 20a can be turned on/off to control gray level status of the corresponding pixel.
For the sake of simplicity, only four TFTs 20a are shown in FIG. 1A, but in practical, there are more TFTs 20a arranged in matrix fashion and each TFT 20a is corresponding to a pixel or a sub pixel. Besides, the circuit characteristics of the liquid crystal cell 10a between two substrates of the LCD panel can be treated as an equivalent capacitor.
However, in the above-demonstrated TFT LCD device, it still needs power to show image, and periodical refresh is also required. Besides, when power is disconnected, the image disappears due to the loss of electrical field across the liquid crystal. This volatile characteristic is very similar to the so-call volatile memory such as DRAM.
FIG. 1B shows the equivalent circuit of TFT 20a for driving a liquid crystal cell 10a, where the liquid crystal cell 10a is treated as an equivalent capacitor. As shown in FIG. 1B, signals sent through word line WL and bit line BL can control the TFT 20a to switching on and off to provide the electrical field across the liquid crystal cell 10a. As DRAM, the implementation in FIG. 1B is volatile and the data in this capacitance is leaky. The stored electrons can leak through the transistor 20a or even get recombined in the semiconductor region. Therefore, the display with light valve such as liquid crystal has the drawbacks of frequent signal refreshing and constant power requirement.